The invention relates to a cutting knife for severing tough, elastic materials, in particular for severing cement beads, e.g. of window panes cemented in motor vehicles or filled in wall joints. The knife comprises a securement portion having a receptacle for securing the cutting knife to an oscillatory drive of a cutting tool, and a cutting portion with at least one cutting edge. The invention further relates to a method for producing such a cutting knife.
A knife of this type is known from EP-B 0 141 035, while similar knives are disclosed in DE-A 3 626 762 and DE-B 3 838 044. It is well known that such cutting knives are used to remove windshields from motor vehicles when this is necessary due to window damage or leakage of the cement bead. A further application is the removal of leaky silicon joints in brickwork.
Common to the known knives is that when cutting through the cement bead, for example when removing a damaged windshield from a motor vehicle, there is considerable danger of breaking the knife. One reason for this is the tough material of the cement bead which is often made of a certain type of polyurethane. Another reason is the considerable force required especially for cutting through thicker beads, despite the high frequency and the small rotary angle of the oscillatory drive. Wider cement beads occur often for windshields that have already been replaced before, where the cement bead has been applied manually during assembly.
On the other hand, such knives or blades become rapidly dull and must be frequently sharpened due to the very resistant and tough material of the cement bead.
The known knives to date are made of a common steel used for knives. Initially, a flat blank is stamped out of a suitable sheet and is optionally bent when the knife is to have a U-shaped cross section or angled or bent form. Optionally a subsequent treatment by grinding follows. Thereafter, the knife is hardened and ground and optionally polished.
The knife disclosed in EP-B 0 141 035 includes a securement opening in the form of a 12-edged hole for form-fit securement to the drive shaft of an oscillatory drive. In contrast, the cutting knife disclosed in DE-A 3 626 762 is welded to the drive shaft. The knives disclosed in DE-B 3 838 044 are fixed to the drive unit as in the manner of a sabre saw and are driven to oscillate in the axial direction. However, such knives are also made from knife steel, hardened and sharpened before use.
In addition, cutting knives are known through prior use whose surface is provided with a thin layer of titanium nitride, which apparently has been applied by chemical vapor deposition. However, such knives have not proven themselves in practice, since the titanium nitride layer is so thin so as to be practically useless. Already after a single re-sharpening, practically no effect remained. In addition, the production using CVD (chemical vapor deposition) is relatively complicated and expensive. Further, the titanium nitride coated knives are also subject to the above-mentioned problems of breakage.
An object of the present invention is to provide an improved cutting knife and a method for producing same, which allows improved cutting capacity and reduced susceptibility to breakage thereby allowing increased utility in operation.
This and other objects of the invention are solved by providing a cutting knife comprising a plurality of flat interconnected layers, where at least two of the layers are of a metallic material. In this manner, the object is achieved in that the multi-layer construction of the knife out of a plurality of individual, flat interconnected metal layers provide improved properties of the knife on the whole. Namely, a particularly high hardness and wear resistance is achieved at the cutting edge or edges and at the same time greatly improved elasticity and reduced breakage is achieved.
It has been known for centuries to produce the so-called Damascus blades, i.e. to produce sabres and daggers from individual layers and to forge these together. Even so, it is not obvious to transfer this method to the production of cutting knives for use in conjunction with an oscillatory drive to cut tough, elastic material.
The cutting knives of the present invention are mass-produced articles which are required in large number in repairing joints in brickwork, in automotive workshops and in glass workshops, since the knives become dull in relatively short time or break. Frequently, a knife can be used only once for cutting out a single windshield.
In contrast, the Damascus blades are handmade and are extremely complicated and expensive in production. Such blades today which consist of numerous individual layers forged together cost three or four digit sums in EUROS. The known knives for use together with oscillatory drives have been used since 1983, however one has not considered the use of a knife with a plurality of metal layers.
It is therefore not obvious to transfer such an expensive and complicated procedure to the production of cutting knives of the present type.
In a preferred embodiment of the present invention, the metal layers are connected to one another by heat bonding, preferably forged to one another.
Although forged metal layers basically have particularly good properties, it is also possible to bond the metal layers in other ways. For example, it is contemplated to surface weld the metal layers, which is possible with a special resistance welding process with simultaneous application of pressure. Friction welding is also possible. More recently, it is also possible to bond the different metal layers for this purpose with adhesives.
In a further embodiment of the present invention, some of the individual layers are made of materials having different properties.
In this manner, the properties of the knife can be xe2x80x9ccustom-madexe2x80x9d in a certain sense. For example, central layers can be provided having a reduced hardness, with high tenacity and bending strength. To the outside, the layers can have an increasing hardness and a decreasing tenacity or bending strength and vice versa. Basically it is possible to provide the different layers out of the same material, but having been treated differently, for example having a different degree of deformation (e.g. using cold rolled or annealed steel). The properties can also be produced when later heat treating the bonded layers. However, it is particularly preferred to use special materials whose composition is adapted to the desired properties. This is to achieve a particularly high elasticity and bending strength in a defined region of the cutting portion and in particular to achieve a high hardness and optionally reduced friction in the outer layers at the cutting edge. In some cases it can also be appropriate to produce the outer layers from a soft and/or particularly elastic material. This is advantageous when the cement bead to be removed is located on a painted surface of plastic or wood.
The outer metal layers can also be subjected to a special surface treatment, for example a treatment with boron, carbon, nitro carbon or the like, to achieve a particular high hardness in the outer layers in the area of the at least one cutting edge.
It is also preferred that at least one of the layers comprises a wear resistant material, preferably wolfram carbide, silicon carbide, titanium carbide, chromium oxide, silicon oxide, titanium oxide, aluminum oxide, boron nitride, titanium nitride, molybdenum or mixtures thereof or mixtures and alloys with further metals.
The additional wear resistant layer is a layer which is not made of the same material as the other metal layers, for example a certain type of steel. Rather, it consists of an inorganic material, normally non-metallic, for example a carbide, an oxide or a nitride. To achieve high hardness and wear resistance, a coating of molybdenum is also contemplated.
These additional layers however cannot be applied as the other metal layers by heat bonding or forging, but require a special coating procedure, for example deposition out of the vapor phase or thermal spraying.
In another embodiment of the invention, at least one of the layers of the cutting portion contains friction reducing additives, preferably segregates of molybdenum sulfide and/or graphite.
The work in severing the cement bead is considerably simplified, since the friction is greatly reduced by the friction reducing additives in the form of microscopically small segregates in at least the outer coating. The operation times are also improved.
In a further embodiment of the invention, at least one outer layer of the cutting portion comprises PTFE (Teflon).
The friction when severing a cement bead is greatly reduced by the anti-sticking effect of PTFE. An adhesive effect of the cement material during severing is counteracted. Due to the reduced friction, the temperature in the severing process is reduced, whereby the tendency to form vapors is also reduced. It can also be advantageous to use colored Teflon to indicate different configurations or to improve the aesthetic impression.
In another advantageous embodiment the cutting portion has blade with a crescent-shaped curvature, which is preferably concavely curved relative to the bearing point. The cutting knife may also have a U-shaped, angled cross section, wherein the cutting portion is connected to the securement portion by an intermediate section, as is principally known in the prior art.
It has turned out that with such geometries of the cutting knife a particularly advantageous severing effect can be achieved, and that with a U-shaped, angled cross section a windshield can be removed from the outside. Beyond that, other shapes are contemplated, e.g. angled or bent blades or cutting knives with a roll as stop, as this is principally known from EP-B-0 174 427.
According to a further embodiment of the invention, the cutting knife comprises a securement receptacle that is configured to be connected to a rotary oscillatory drive. In an alternative embodiment of the invention the cutting knife comprises a securement receptacle that is configured to be connected to an oscillatory drive which oscillates in an axial direction.
The cutting knife according to the invention can be advantageously used with both of these securement receptacles.
In a further embodiment the cutting knife has a core region comprising an elastic material and/or soft material.
In another embodiment based thereon, the knife comprises a cutting portion which is provided with the different layers only in the region of the at least one cutting edge.
These measures simplify fabrication of the knife because the core region of elastic and/or soft material can be produced in a relatively simple manner for example by stamping out of a sheet. Simultaneously, a securement receptacle in the form of an opening can also be stamped out, where then the various layers can be applied to the cutting portion to achieve the required properties. If the cutting knife also contains an intermediate portion, the additional layers can naturally also be extended thereto, for example to achieve a high tenacity and bending strength in the region of the intermediate portion.
In this manner, the production is simplified and the production costs are considerably reduced.
According to the present invention, a method is also provided for producing a cutting knife for severing tough, elastic materials, in particular for severing through cement beads e.g. of window panes cemented in motor vehicles, with a securement receptacle for securing the cutting knife to an oscillatory drive of a cutting tool, and a cutting portion with at least one cutting edge. The method comprises the steps of
a) producing a plurality of metal layers,
b) heat-bonding the metal layers, preferably by forging, to produce a metal blank for the cutting knife,
c) heat-treating the blank to improve the hardness and/or break resistance, preferably by hardening and tempering the blank,
d) sharpening of the blank by grinding and/or by polishing to produce said at least one cutting edge.
In this way the knife of the present invention is produced with distinctly improved properties which unite a high stability, in particular high tenacity and bending strength with a good hardness and wear-resistance of the cutting edge or edges.
It will be understood that the individual metal layers can be made of differently alloyed metals.
A forging process is preferably used for heat bonding the layers, i.e. bonding with a corresponding high temperature under pressure by hammering or the like. Further, it is contemplated to generate the bond with presses and sufficiently high temperature, as long as the pressing machines are mechanically and thermally stable. It is also possible to form the intimate bond by friction welding or with a special resistance welding procedure while additionally applying surface pressure.
In a preferred embodiment of the present method, the securement opening is formed after the heat treatment of step (c), preferably by electric erosion or laser cutting.
It is difficult when producing the blank by heat bonding several metal layers to achieve the desired dimensions for the securement receptacle, which can for example be an opening in the form of a multi-edged hole, for example a 12-edged hole. The production method is simplified in that a flat metallic blank is initially produced in a suitable process, which can be heat-treated in a suitable manner to obtain the desired mechanical properties, wear resistance and hardness. A spark erosion process or a laser cutting process are suitable for producing the securement receptacle as an opening in relatively inexpensive manner but with sufficiently accurate dimensions.
If the cutting knife should not be flat, but have a certain bending, the blank is bent in the heated state before the heat treatment for improving the hardness and/or break resistance, where a hardening and tempering follows. When using steel, the bending should preferably take place in the red-glowing condition.
Alternative to the above-described method, the knife can be produced from a blank of elastic and/or soft material, where the plurality of metal layers is applied at least to the region of its at least one cutting edge.
As explained above, the production method is simplified and considerably less expensive. Namely, in a further embodiment the blank can be produced of elastic and/or soft material together with the securement receptacle for example by stamping. The various metal layers are used only in the region where special improved properties are necessary, in particular in the region of the cutting portion and optionally the region of the intermediate portion.
If the metal layers are only applied to the cutting portion, the bending to produce a angled U-shaped or bent knife can be performed in the cold condition.
In a further embodiment of the present method, at least one additional wear resistant layer is applied to the cutting portion.
Preferably this layer can be of wolfram carbide, silicon carbide, titanium carbide, chrome oxide, silicon oxide, titanium oxide, aluminum oxide, boron nitride, titanium nitride, molybdenum or mixtures and alloys with further metals.
As mentioned above, a knife with a particularly hard and wear resistant blade can be produced in this manner, however still having sufficient elasticity and bending strength.
The wear resistant layer or layers are preferably applied by deposition from the gas phase (CVD or PVD) or by thermal spraying, preferably plasma spraying.
While only very thin layers can be applied with the CVD or PVD methods, which are complicated and expensive, the use of a thermal spraying process allows a very dense coating with a greater thickness in the range of up to about 1 millimeter.
Only a sufficient thickness of the coating in at least the region of the at least one cutting edge leads to the distinctly improved cutting properties of the knife. A coating of lesser thickness of few micrometers would lose its effect already at the first sharpening or with subsequent sharpenings, since it would be completely removed from the cutting edge.
In a further embodiment of the present method, the wear resistance layer is produced by thermal spraying of carbides in a metal matrix, preferably in nickel, cobalt or alloys thereof.
In this manner, carbides can also be thermally sprayed, where the preferred matrix of nickel, cobalt and other alloys will normally comprise carbide additives in an amount of between 8 and 30 weight percent. When melting the matrix in the flame, it reacts with the carbide to form various mixed phases. Wolfram carbide layers, chromium carbide layers or metal carbides are contemplated. If oxide layers are produced by thermal spraying, their properties can also be improved by mixing and forming alloys. An aluminum oxide layer can be employed mixed with 3 to 40 weight percent titanium oxide, which produces a relatively high hardness with reduced brittleness.
In another embodiment of the present method, friction reducing additives are added to the wear resistant layer. For example, these can be microscopically small segregates of molybdenum sulfide and/or graphite. However, due to the danger of oxidation, a spray application must be done with a protective gas.
In an alternative embodiment of the invention, the method for producing a cutting knife comprises the following steps:
a) producing a blank made of steel,
b) heat-treating the blank to produce a high elasticity and break resistance, preferably by tempering the blank,
c) sharpening the blank, preferably by grinding and/or polishing,
d) applying at least one wear resistant layer to the cutting portion by thermal spraying.
In this manner, a knife can be produced with high elasticity and break resistance which simultaneously has good severing properties.
Compared to the production with a plurality of metal layers, this method is considerably less expensive because the complicated process of heat bonding, for example by forging the individual layers, is no longer present.
In addition, the knife can be produced in the conventional way with a suitable knife steel, which however is subjected to a special heat treatment to achieve a high elasticity break resistance, i.e. not the normal hardening as with conventional knives. An annealing or tempering can follow the hardening to achieve an increase bending strength and elasticity with reduced hardness, as well as an improved break resistance.
The normally insufficient hardness in the region of the at least one cutting edge of such knives is now overcome by the application of a wear resistant layer by thermal spraying. A layer of sufficient thickness can be achieved with the spraying process, so that exceptionally good cutting properties can be achieved in the region of the cutting edge, i.e. a high hardness and wear resistance, even despite the insufficient hardness of the blank.
The wear resistant layer can be produced of molybdenum, a carbide, an oxide, a metal carbide, a metal oxide or mixtures thereof.
As mentioned above, it is again particularly preferred to apply the wear resistant layer by thermal spraying of the carbides, which are contained in a metal matrix, preferably of nickel, cobalt or alloys thereof.
In a further embodiment of the invention, the blank is jet beam roughened before the thermal spraying.
This allows an improved adherence of the thermally sprayed layer to the surface of the blank.
In another embodiment, a layer of bonding agent is applied before spraying on the wear resistant layer.
This provides a further improved adherence of the wear resistant layer to the knife, where disadvantages caused by the differences in thermal expansion coefficients can be partially compensated.
In another preferred embodiment of the present method, the securement receptacle is produced by stamping.
The production process is distinctly simplified and less expensive, as in the case of the conventional production of such knives, however without having improved properties.
In case an angled cross section is to be produced, a bending takes place before the heat treatment according to step (b).
As above, friction reducing additives can be added to the wear resistant layer, preferably segregates of molybdenum sulfide and/or graphite.
It will be understood that the above-mentioned and following features of the invention are not limited to the given combinations, but are applicable in other combinations or taken alone without departing from the scope of the invention.